Technical Field
The present invention relates to a signal amplifier amplifying plural sensor signals having amplitude levels in accordance with a rotational position of a rotor of a motor to have specified amplitude levels, and a phase detector and a motor drive controller equipped with the signal amplifier.
Description of the Related Art
It is necessary to detect a rotational angle of a rotor to control a rotational position of a motor. The rotational angle of a rotor is typically detected by a rotary encoder connected with a rotational axis of the rotor. In this case, the rotary encoder produces a 2-phase pulse signal varying in accordance with the rotational angle of the rotor and having a phase difference of 1/4 cycle. A relative rotational angle is detected from the edge detection and a High/Low status of the 2-phase.
An optical encoder as the rotary encoder is formed of a disc having slits as optical windows located at an equal interval on the outer circumference and two photo-interrupters located at a 1/4 interval of a split pitch of the disc. Signals produced from the two photo-interrupters are binarized to obtain the 2-phase pulse signal.
Japanese published unexamined application No. JP-2013-99023-A discloses a drive motor controller, in which plural sensor signals having signal levels in accordance with the rotational angle of the rotor are used to detect a phase information signal. Namely, since each of the sensor signals does not have a uniform common level and amplitude level, an amplitude level of each of the sensor signals is detected. The detected amplitude level is amplified to have a specified amplitude level such that each of the sensor signals have an ideal sine wave. A phase information signal is detected, based on the sensor signal, the amplitude of which is adjusted.
However, in the motor drive controller, the sensor signal varies in amplitude at every pole even in a one cycle of the motor due to uneven magnetization of a magnet used in the rotor. Therefore, when the amplitude of each of the sensor signals is uniformly adjusted, each of the sensor signals does not have an ideal sine wave, and the phase information signal cannot precisely be detected, based on each of the sensor signals.